Combustion responsive device especially suitable for use in controlling the operation of a fuel burner



3,351,725 R USE IN D F. GIBSON Nov. 7,1967

COMBUSTION RESPONSIVE DEVICE ESPECIALLY SUITABLE F0 CONTROLLING THEOPERATION OF A FUEL BURNER Filed March 18, 1966 3 Sheets-Sheet 1INVENTOR. flaw'a/Fffiwsom Y Z.

Attorney- Nov. 7, 1967 3,351,725 R USE IN D. F. GIBSON COMBUSTIONRESPONSIVE DEVICE ESPECIALLY SUITABLE F0 HE OPERATION OF A FUEL BURNERCONTROLLING T Filed March '18, 1966 3 Sheets-Sheet 2 Dav//FG/bs on,

NovQ7, 1967 I COMBUSTION RESPONSIVE D Filed March 18, 196

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United States Patent l 3,351,725 COIWBUSTION RESPONSIVE DEVICEESPECIALLY SUITABLE FOR USE IN CONTROLLING THE OPERATION OF A FUELBURNER David F. Gibson, Sterling, Ill., assignor to General ElectricCompany, a corporation of New York Filed Mar. 18, 1966, Ser. No. 535,58412 Claims. (Cl. 200137) ABSTRACT OF THE DISCLOSURE This inventionrelates to combustion responsive devices, and more particularly to animproved combustion responsive device especially suitable for use incontrolling the operation of a fuel burner, such as a gas burner.

In the type of controls normally used for-operating fuel burners, as forexample, a gas burner in a' clothes dryer, space heater and other gasfired equipment, it is customary to initiate combustion of fuel by anelectric igniter having electrodes disposed near the burner outlet inproper location with respect to the fuel stream. The presence or absenceof a burner flame at the burneroutlet is signaled to other components ofthe control device by a so-called thermally responsive flame detectorassembly which has a temperature sensor deployed in proximity to and inheat exchange relation with the burner flame at the burner outlet. Byway of illustration, in one kind of fuel burner control device,the'presence of a flame in the vicinity of the temperature sensor causesthe assembly to actuate at least one combustion switch mounted at alocation remote from the burner outlet. The switch in turninterruptscurrent to the electric ignitor to turn it off. The fuelburner controls disclosed in Patent 3,207,204 granted to P. W. Thompsonon Sept. 21, 1965, and in Patent 3,155,144 granted to S. J. Budlane onNov. 3, 1964, are representative of this general approach.

In the actual practice of such approach, there has been a practicaldifliculty or problem in providing an economical, yet rapidly respondingand simply constructed flame detector assembly for utilization in thesatisfactory control of fuel burner operation. In particular, inaddition to the continuing problems associated with ,the attainment oflow cost and simplification of construction, there is a need for a flamedetector assembly which responds quickly and with minimum variation inconnection with any number of different fuel-air flow input rates which,in turn, produce a multitude of diverse operatingcombustion conditionsin the same burner and a wide variation in the operating temperature atthe temperature sensor portion of the flame detector assembly. It isfurther desirable that the assembly be constructed such that it not onlyfurnishes the above features, but also permits disposition of thetemperature sensor in a lower temperature region of the fuel burnerflame without appreciably interfering with the proper operation of theassembly. 7

Consequently, it is a primary object of the present invention to providean improved combustion responsive device and in particular, a deviceespecially suitable for utilization in controlling the operation of fuelburners.

It is another object of the present invention to provide an improvedflame detector assembly which furnishes the desirable features andovercomes the problems mentioned heretofore.

It is still another object of the present invention to provide animproved flame detector assembly which permits economy andsimplification in its manufacture and con struction, is easy to install,is versatile in application, and responds rapidly and with minimumvariation to a number of diverse operating combustion conditions.

It is a further object of the present invention to provide an improvedflame detector assembly of the type operating on a differentialtemperature-expansion principle and which includes a novel temperaturesensorwhich achieves greater temperature differential at variousoperating combustion conditions than was possible with previoustemperature sensors.

It is a final object of this invention to provide a fuel burner unitutilizing the flame detector assembly of the instant invention.

In carrying out the invention in one form, I provide an improvedcombustion responsive device especially suitable for use in the controlof a gas burner of the type normally used in clothes dryers or the like.The combustion responsive device includes a flame detector assemblyhaving a temperature sensor in the form of an elongate body member ofnon-circular cross section and formed from a single flat sheet ofmetallic material characterized by relatively low thermal conductivity,together with a mechanical lever suitably mounted in the body member forswitch actuation upon difierential expansion of the body member. Thetemperature sensor, in this one illustrated exemplification of theinvention, is of generally triangular cross section, including a basewall section mounted so as to present a temperature sensitive region toa burner flame, a pair of converging side wall sections includinggenerally parallel free edge portions, and outwardly diverging coolingfins on the free edge portions of the wall sections disposed in opposedrelation to the temperature sensitive region. The cooling fins arenormally located in a portion of the heating chamber in which the burneroutlet and flame detector assembly are mounted which receives coolingair due primarily to a secondary air flow therethrough. as well asconvection air currents caused by the burning ,gases. Thus, such coolingfins eliminate the necessity for an elaborate and expensive flame shieldgenerally required by prior art devices in order to achieve thenecesfied form of the triangular body member with cooling fins,

will adequately function when located in a relatively cool part of theburner flame, and thus will have an extended useful life. Further, costreduction is effected as the sensor may be'quickly and inexpensivelyfabricated of flat sheet stock material rather than the round or tubularstock used in the prior art sensors, and also may be more readilyassembled.

The body member is supported at one end on a'stationany support, theother end of the member being free, in a cantilevered fashion. The.aforementioned mechanical lever comprises a switch actuator arm which isfixedly mounted at the free end. of the body member, the arm extendingthrough the body member and past the supported end thereof and includingsuitable switch actuating means at the free end thereof. Theswitchestare located in a control section of the combustion responsivedevice,

readily appreciated, they could also be normally open. The detectorassembly operates on a principle of differential temperature expansion,wherein when the temperature sensitive region of the sensor or bodymember is exposed to the burner flame, it will be rapidly heated therebyand hence expand, while the opposed portion of the body member, byvirtue of various factors to be explained more fully below, will beheated more slowly and hence expand at a relatively slower rate. Thisuneven expansion of the body member will cause deflection thereof,which, although very slight is greatly magnified by the switch actuatorarm in order to actuate the aforementioned switches in the controlportion of the device.

Further aspects of the invention will become apparent from the moredetailed description of the invention which follows. It will beunderstood that the specification concludes with claims whichparticularly point out and distinctly claim the subject matter which Iregard as my invention. The invention, however, both as to organizationand method of operation, may be best understood with reference to thefollowing description taken in connection with the accompanying drawingsin which:

FIGURE 1 is a perspective view of a burner mounted combustion responsivecontrol unit embodying one form of my invention;

FIGURE 2 is a perspective view similar to that of FIG- URE 1illustrating the control unit as well as a flame pattern for onecondition of combustion emanating from the burner;

FIGURE 3 is a horizontal sectional view taken substantially on the planeof the line 3-3 of FIGURE 1;

FIGURE 4 is an exploded perspective view of the various components ofthe combustion responsive unit comprising one form of my invention;

FIGURES 5 and 6 are graphic representations of various operatingcharacteristics of the flame detector assembly illustrated in FIGURES1-4 above, the sensor member being of a specified size, as compared to aprior art flame detector assembly having a sensor member of comparablesize, illustrating the favorable manner of operation of my invention;and

FIGURE 7 is an enlarged vertical sectional view taken substantially onthe plane of the line 7-7 of FIGURE 3.

Referring now more specifically to the drawings, and particularly toFIGURES 14, reference numeral 10 generally denotes a combustionresponsive control unit for a gas burner 12. The unit 10 includes acontrol generally denoted by reference numeral 14 of the general typeset forth in the aforementioned Thompson Patent No. 3,207,- 204, anigniter 16 of the general type illustrated in Patent No. 3,147,401granted to G. H. Wotring on Sept. 1, 1964, and a combustion of flamedetector assembly 18 of the general type as shown in the aforementionedBudlane Patent No. 3,155,144.

The control unit 10 has a basic bracket support 19 upon which thevarious operating components are mounted, the bracket support 19 havingsuitable means 20 thereon for enabling the unit 10 to be mounted on theburner 12 adjacent tthe burner outlet port 22. The burner 12 of theexemplification is generally conventional in construction, comprising anelongated and rigid tubular casing 24 forming a burner chamber 26therein terminating in outlet port 22. A suitable baflie 28 is mountedover the outlet port 22 in order to provide a desired flame pattern, theflame pattern being best illustrated in FIGURES 2 and 3 and denoted byreference numeral 30. It will be understood that the illustrated burneris used by way of example only, and that the exemplified control unitmay be used with various other burner embodiments, such as for example ahorizontal type of burner having a plurality of ports therein fordirecting jet flame upwardly therefrom.

Reference may be made to the aforementioned Thompson patent for adescription of the specific operation of the control 14. However, forpurposes of explaining this invention it will be seen that the control14 includes a U-shaped supporting bracket 32 which is mounted on thebracket support 19 by suitable mounting means, the supporting bracket 32including a pair of parallel supporting legs 34 and 36. It will beunderstood that the control 14 includes a cover which has been left oifso as to better illustrate the operating components thereof. The control14 includes one or more combustion switches 38, only one of which isschematically illustrated in FIGURE 3. The switch 38 includes a pair ofsupporting arms 37 and 39, carried in a supporting stack 41, one of thearms being normally flexible. In this instance, arm 37 is flexible so asto be responsive to applied force thereon. Each arm 37 and 39 carries acontact button 40 at the outermost or distal end thereof. The switch 38is provided to control the operation of a lookout device (notillustrated) in accordance with the preferred operation of the Thompsonpatent, No. 3,207,204. Further, the switch 38, when actuated, interruptscurrent to igniter 16 to turn it off.

The igniter 16 is disclosed in the aforementioned Wotring patent andspecifically described therein. For purposes of explaining thisinvention, it will be seen that the igniter 16 includes a pair ofelectrodes, a stationary electrode 42 and a movable electrode 44. Theelectrodes 42 and 44 are disposed in the general area forward of burneroutlet port 22 as the igniter 16 is supported in depending relation frombracket support 19, in order to provide ignition means for the burner.The electrodes 42 and 44, respectively, include electrode contacts 46and 48 mounted on the forward ends thereof. Thus, when the electrode 44is moved away from electrode 42 in accordance with the operation of theigniter 16, an arc will be formed between the contacts 46 and 48 toignite the gases from burner 12.

The flame detector assembly 18 is provided in the control unit 10 inorder to indicate the presence or absence of flame at the burner outletport 22. The flame detector assembly 18 is responsive to the flamecondition of the burner 12 for operating the switches 38 in control 14,so that the control may automatically regulate the igniter 16 as well asautomatically control the supply of gases to burner 12. The assembly 18comprises a combustion responsive sensor element generally denoted byreference numeral 52, which in this exemplification of the invention isin the form of an elongate longitudinally extending differentialtemperature expansion body member of non-circular cross section. Thebody or sensor member 52 includes a base wall section 54 and a pair ofgenerally non-parallel or converging side wall sections 56 and 58. Themember 52 is formed from a sing-1e piece of sheet metal material, suchas stainless steel or the like so as to have a low thermal conductivity.It will be understood, of course, that the member 52 may be formed fromany suitable material characterized by low thermal conductivity. Onesuch suitable metal is stainless steel which has a thermal conductivityof 12.8 B.t.u./sq. ft./hr./ F./ ft. (932 F.).

The member 52 is fixedly mounted in a generally triangular-shapedaperture 60 in the leg 34 of supporting bracket 32, the aperture beingbest illustrated in FIG- URE 4. It will be seen that the aperture 60includes an additional projection portion 62 for a purpose to be morefully discussed below. The particular configuration of the body member52 allows it to be quite rigidly supported in the leg 34 even though themember is supported in canti lever fashion. Each wall section of thebody member is supported against one edge of the aperture, and themember 52 is secured firmly in place by spot welds or other suitablesecurement means. Thus, member 52 is supported at each face or surfaceadjacent one end thereof.

The illustrated configuration of the body member 52 provides optimumoperating results due to the relatively thin material used for theconstruction thereof. Thus, the thin-walled construction of the bodymember allows optimum response to differential temperatures, and theminimum mass thereof provides low thermal conductivity.

However, in spite of the use of this thin material and also thecantilevered support of member 52, an unusually rigid member is providedby this construction. 7 It will be observed that, as ilhrstrated, thebodymember 52 is preferably stamped from a single piece of portions 64and 66 of the side wall sections 56 and 58, {5

respectively are flattened out or bent so as to be pgall in order toprovide fastening ears for an @ngate switch actuating arm 68.

The actuating arm 68 is an elfigate arm preferably 52, with the sidewall sections converging inwardly away from the flame for burner 12,will prevent the flame from enveloping the member. Thus, while the flamemay impinge directly on the base wall section, and specifically on thetemperature sensitive region 94, the tendency to goaround the corners 59and 61 is reduced and the flames impingement directly :upon the sidewallsections 56 and 58 is reduced (see FIGURE 2 for example). Thisconstruction, along with the low thermal conductivity ofthe tion of theassembly 18. Furthe actuating arm 68 is constructed, in tlyxe iicationof the invention, of material ha ing r'elatively greater thermal massthan the ernbfi 52, and since the arm is fixed directly to the base wallsection 54 by a weld, which affords a ready heat flow path, the arm 68will act as a heat sink and will conduct heat away from the side wallsections 56 and 58.

Referring again to FIGURES 3 and 4 as well as to 0 material of whichmember 52 is composed will create necessary temperature gradient in theme ior operaformed of a metallic material having suitable thermal 0FIGURE 7, it ill b ob r d that a pair of cooling conductive qualities aswell as rigidity or strength, the arm including a flat fastening tabportion having a projecting nose 72 thereon and a longitudinallyextending strengthening rib 74 therein. Referring to FIGURE 3 fins 82and 84 are integrally formed at the unsecured longitudinal edges of theconverging side wall sections 56 and 58 intermediate the secured andfree ends of member 52. The cooling fins are provided to augment the inParticular, it Will be Observed that the fastening tab above mentionedfeatures of, the inventionfor maintainportion 70 is disposed in the freeend 71 of the sensor or body member 52, this free end being opposite theend supported in leg 34. The nose 72 abuts the base wall section 54 andthe fastening ears 64 and 66 sandwich the sides of the tab 70. The arm68 is thus spot welded or otherwise suitably mounted in this positionwith ears 64 and 66 being spot welded. to the tab 70 and the base wall54 spot welded tovnose portion 72.-The arm is thereby rigidly mounted atone end in the body or sensor member 52.

3 Referring again to FIGURE 3, it will be observed that the actuator arm68 extends through the member 52 and through the aperture 60 into thecontrol 14. Of course, it will be appreciated that the majority of thecontrol elements orcomponents have been left out of FIGURE 3 forpurposes of illustrating the movement of the free endof arm 68. It willbe seen that the arm 68 extends past the switch supporting stack 41 andthat the arm includes a generally L-shaped bracket 80 on the free endthereof. The bracket 80 has a threaded actuating screw 78 adjustablymounted therein, the screw 78. extending into control 14 so as to engagethe switch button 40 upon actuation of the detector assembly 18. Theswitch 38 includes switch contacts 79 and 81 respectively carried onrigid and flexible arms 39, 37. The contacts in this instance arenormally. closed so as to maintain the switch 38 closed. The actuatingscrew 78 is adapted to abut theswitch button 40 so as to bend apart thearms 37 and 39 and open the contacts 79, 81and hence switch 38 inresponse to flame detection, and is threaded so as to, be adjustable inthe initial position thereof in bracket 80.

In accordance with the operating principles of my invention, adiiferential temperature occurs in the sensor member 52 between atemperature sensitive region or zone 94 of the base wall section 54 anda region or zone 60 on the opposite side of'the member SZremote from theregion 94. This differential temperature will causedifferentialexpansion in the member and thus deflection at the free end 71 about themounting leg 34. The actuator arm 68 is provided to greatly magnify'thisslight deflection at the free end 71 of member 52, the arm being mountedat this end and extending into control 14 and carrying the actuatingscrew 78 at the free end thereof. Since'it is necessary to achievetemperature dilferential in the sensor member 52, the temperaturesensitive region must be thermally isolated from the opposed side of themember. This isolation is achieved in several ways in accordance withthe novel aspects of my invention. By referring to FIGURES 2 and 3 inparticular, it Will be observed that the particular construction of themember 75 ing a temperature gradient in the body member 52 duringoperation. The arms 82 and 84 diverging outwardly, as is bestillustrated in FIGURE 7, in order to provide the maximum accessibilityto air flow thereover for purposes of 'cooling'The particular surfacearea of the fins will depend, of course, upon the particular applicationto be made of the member 52.

By referring again to FIGURE 3 in particular, it will be understood thatthe sensor member 52 may be dis- 5 posed in a heating chamber adjacentthe burner outlet port 22. While the chamber'is not fully illustrated,'aportion thereof in the form of wall 86 of a cylinder or other suitablemeans is shown for purposes of explanation. Thus, only the free end 71of the member 52 will be subjected to the flame from the burner 12, itbeing'desirable to isolate the other operating elements of the controlunit 10 from the flame-In this regard, a'bafile 88 in the form of agenerally L-shaped member is mounted on the sensor member to control theflame pattern 30. One leg 90 of the baifle is attached to the base wallsection 54 as best illustrated in FIGURE 3, and the other leg 92 thereofis disposed substantially adjacent the outlet port 22 to direct theflame pattern 30 in the manner illustrated in FIGURE 3. The bafl le 88is mounted transversely across the base wall section 54 in order toconcentrate the flame from burner 12 near the free end 71 of member 52,and to isolate the flame from control 14. The baffle 88 acts to createturbulence adjacent the temperature sensitive region 94 of base wallsection 54 so as to pull the flame onto the wall 54 and hence the baflleproduces impingement of the flame on the sensor element 52.

A number of flame detector assemblies have been built in accordance withthe illustrated exemplification of my invention. The body member wasconstructed of 0.015 inch thick stainless steel, the member beingapproximately 3.5 inches in length and the'arm 68 being approximately5.5 inches in length (nominal dimensions);

. It has been found during testing of these assemblies that a' 'steadystate difierential temperature of 200 -300 65 Fahrenheitis possibleunder certain operating conditions,

and that this temperature'dilferential or gradientreadily provides foroperation of the device in the manner intended. a

The flame detector assembly18 is readily mounted in 94 7 place in theunit 10 with the sensor or body member 52 fixedly mounted at one end tothe leg 34 with the other end 71 being free in cantilevered fashion. Theactuator arm 68 is fixedly mounted in the free end 71 extendingcompletely through the member and aperture to a position'within thecontrol 14. The sensor member 52 is positioned to present thetemperature sensitive region 94 of base wall section 54 to the flamefrom the burner 12, it being illustrated in FIGURE 2, for example, thatthe flame pattern 30, will strike the temperature sensitive region 94,but will not impinge on the side wall sections 56 and 58. The member 52was placed in the actual assemblies in the path of the flame pattern tobe sensed so that the temperature sensitive region 94 was atapproximately a 45 degree angle to the direction of the flamesimpingement. Thus, the member 52 was not placed in the hottest part .ofthe flame as it will readily function while supported in a coolerportion of the flame, for example, in a portion ranging from 092 135?Fahrenheit. This will obviously increase the useful lifeof the detectorassembly. As mentioned above, the temperature dilferential or gradientbetween the temperature sensitive region 94 and the opposed side of thesensor member 52 was in the range of approximately 200-300 Fahrenheit atsteady state, this being sufficient to cause unequal expansion in themember 52 and hence deflection about the leg 34.

The temperature differential or gradient occurs in the member 52 forseveral reasons: First the particular configuration of the side wallsections 54 and 58 will prevent direct impingement of the flame thereon.Second, the cooling fins 82 and 84 will be primarily cooled by asecondary air flow through the heating chamber as well as by aspiratedair. Third, the body member is composed of material which has lowthermal conductivity, and hence the heat applied to region 94 will notbe readily conducted through the member. Fourth, the actuating arm 6%acts as a heat sink to conduct heat away from the side wall sections 56and 58.

The movement of the free end of actuator arm 68 in control 14 in thisexemplification of the invention may be best appreciated by referring toFIGURE 3 wherein it is shown that the right end of the arm 68, the endat which the adjustable actuating screw 78 is supported, will moveupwardly a good deal further than the movement at free end '71 of member52, the arm 68 acting to multiply the motion at end 71, thus moving thecontact button 82 from the position illustrated by lines in full to theposition illustrated by lines in ghosts in order to open the switchcontacts 79 and 31. Such movement of arm 68 is facilitated by theprojecting portion 62 of aperture 60 referred to supra. In theconstructed assemblies, the movement at screw 78 was .025 inch minimum,which will cause the switch contacts '79 and 81 to open inasmuch as thecontacts will open upon relative movement therebetween of .008.0l6 inch.

With the above discussion of my instant invention in mind, reference isnow made to FIGURES 5 and 6 wherein the advantageous operatingcharacteristics of my sensor are graphically illustrated. Referringfirst to FIGURE 5, the full line curves are representative of thedeflection of a number of tests made on my actual sensor members, of thetype described above, under various combustion conditions in relation totime. The broken line curves indicate the characteristics of a prior artsensor of the tubular type and the same general size as my sensor, theprior art sensor also including a complex flame shield for coolingpurposes. It was determined that it is most desirable to obtain maximumdeflection in the shortest amount of time, with the primary objectivebeing to obtain an average deflection of .018 inch in as short a time aspossible under a variety of different combustion heating condi tions. Asillustrated in FIGURE 5, upon actual testing of the prior art sensor andmy sensor taken under the same general conditions and used with the sametype control units, it will be noted that there is less responsevariation in my sensor member 52 under a number of diverse operatingcombustion heating conditions than in the prior art sensor for the sameconditions. It will also become apparent from FIGURE 5 that my sensormember normally reaches .018 inch deflection sooner than the prior artsensor, and thus has more desirable operating characteristics and lessvariation or deviation than this prior art device.

As stated above, it is desirable to reach .018 inch deflection at thescrew 78 as soon as possible. However, while such deflection willusually open the switch contacts 79 and 81, a significant reduction intemperature gradient in the member 52 may cause enough reverse movementof the actuator arm to allow the contacts to close. However, it isdesirable to reach steady state conditions as soon as possible, underwhich conditions the deflection at the screw 78 will be greater than.018 inch, and thus prevent such problems of recycling. Accordingly,reference is now made to FIGURE 6, wherein there is illustrated thedeflection of the two above referred to sensor members plotted against asteady state gas input rate, my sensor member 52 again being representedby the lines in full and the prior art sensor represented by the brokenlines. The steady state gas inputrate may be as low as 6,000 B.t.u. perhour for some applications, and with my sensor, superior results will benoted at these low input heating conditions, where satisfactory resultsare quite diflicult to obtain. Thus, it will be readily apparent fromFIGURE 6 that at the low end of the heating cycle especially, my sensormember achieves consistently better results than the prior art device.

Incidentally, it should be understood that, while specific reference hasbeen made to the heating cycle of the burner and the attendant operationof my sensor, my sensor achieves similar advantageous operations duringthe cooling cycle. Further, it will be readily apparent that thedetector assembly responds in a substantially similar, but reversemanner during the cooling cycle.

It will be apparent from the foregoing that my flame detector assemblymakes it possible to achieve rapid and uniform response to a member ofdiverse operating combustion conditions for controlling a gas burner.Further, my detector may be economically constructed from a wide rangeof readily available materials and easily assembled and mounted for usein a control unit. Still further, the advantages attained by myinvention are available, while the total cost thereof is lower than thecost of flame detection devices generally used in the prior art.

While the present invention has been described by reference to theparticular embodiment thereof, it is to be understood that manymodifications may be made to the improved flame detector assembly bythose skilled in the art without actually departing from my invention.It is, therefore, intended in the following claims to cover all suchequivalent variations as fall within the true spirit and scope of thisinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A flame detector assembly for detecting the presence of a flame at aburner outlet of 'a fuel burner unit and for transmitting the detectionto a switch means for controlling the fuel =burner unit; said assemblycom-prising, an elongate longitudinally extending temperaturedifferential expansion member having a base wall section, said base wallsection joined to a pair of generally nonparallel side wall sections,one end of said member being fixedly attached to a stationary support,the other end of said member being free and formed by at least a portionof said sections with a part of the base wall section providing atemperature sensitive region adapted to be disposed in the vicinity ofthe burner outlet, an elongate switch actuator arm having one endsecured to said free end of said member and having a free end projectingbeyond said one end of said member, actuator means carried substantiallyadjacent said free end of said actuator arm for actuating the switchmeans in response to movement of said actuator arm, and cooling meansassociated with said member in opposed relation to said temperaturesensitive region for maintaining a preselected region of said memberspaced from the temperature sensitive region at a relatively lowertemperature than said temperature sensitive region whereby said memberwill readily respond to application of heat from the burner flame.

2. The flame detector assembly of claim 1 wherein said side wallsections generally converge and include generally parallel spaced apartedge portions opposite their juncture to said base Wall section, saidcooling means comprising a pair of cooling fins, each of said coolingfins integrally formed with one of said side wall sections and extendingoutwardly from said edge portions.

3. The assembly of claim 2 wherein said cooling fins are attached atsaid edge portions and diverge outwardly from the side Wall sections.

4. The assembly of claim 1 wherein said member is formed of sheetmaterial characterized by low thermal conductivity.

5. The assembly of claim 1 wherein said member is formed from a singlepiece of said sheet material, and mem-ber being generally triangular incross section, said actuator arm having a major portion of its lengthcontained within the confines of said member and a minor portion of itslength without the confines of said member, said actuator means on saidminor portion.

6. The assembly of claim 5 wherein said converging side wall sectionsinclude generally parallel spaced apart edge portions opposite theirjuncture with said base wall section, said cooling means comprising atleast one cooling fin, said cooling fin integrally formed with one ofsaid side wall sections and extending outwardly from said edge portion.

7. In a fuel burner unit having a fuel burner outlet port means, meansfor controlling the fuel supply to the unit, and means for initiatingcombustion of the fuel to produce a burner flame; a temperatureresponsive device comprising, an elongate temperature differentialexpansion member having a non-circular cross section and being formedfrom a single piece of sheet material of relatively low thermalconductivity, said member including a base wall section adapted to bedisposed in the vicinity of the burner outlet port means wherein theburner flame will impinge upon the base wall section and a pair of sidewall sections each having one longitudinal edge integrally joined tosaid base wall section, said member supported at one end and free at theother end, a switch actuator arm, said arm rigidly attached at one endto the free end of said member and the other end of said arm extendingthrough said member beyond the supported end thereof, and switchactuating means on said other end of said arm.

8. The temperature responsive device of claim 7 wherein at least aportion of said sidewall sections converge inwardly from .saidlongitudinal edges, and another portion of said side wall sectionsadjacent the free end of said member being generally parallel andsupporting a portion of said arm.

9. The temperature responsive device of claim 8 wherein said inwardlyconverging side wall sections terminate in unsecured longitudinal edges,and cooling means integrally joined to at least one of said unsecuredlongitudinal edges for maintaining said unsecured longitudinal edge at arelatively lower temperature than said base wall section.

10. The temperature responsive device of claim 9 wherein said coolingmeans comprises a cooling fin extending outwardly from said unsecuredlongitudinal edge, said cooling fin being substantially planar in shapeand adapted to be disposed in a cooling air stream for cooling thereof.

11. A temperature difierential responsive device comprising. a sensingelement; means for supporting said element at one end only; said sensingelement formed from a single piece of sheet material characterized byrelatively low thermal conductivity; said sensing element including, abase wall section having a temperature sensitive region adapted to bedisposed in the vicinity of a source of heat, and a pair of convergingside wall sections intermediate the end-s of said sensing element, onelongitudinal edge of each side wall section integrally joined to saidbase wall section, said side wall sections terminating in parallelunsecured longitudinal edges; switch actuating arm means having a firstend attached to said base wall section and to a portion of at least oneof said side wall sections at the end of said element remote from saidsupported end, said arm extending through said sensing element andhaving a second free end; switch actuating means on said second free endfor actuating switches in response to deflection of said sensing elementabout the supported end thereof.

12. The temperature responsive device of claim 11 including at least onecooling means integrally joined to one of said side wall sections at theunsecured longitudinal edge thereof, said cooling means beingsubstantially shorter than said unsecured edge and extending lateral-1youtwardly therefrom and adapted to be disposed in a cooling air streamfor cooling thereof.

References Cited UNITED STATES PATENTS 2,266,721 12/ 1941 Christiansen200-137 2,392,065 l/ 1946 Rodgers 200-137 2,494,660 1/1950 Kathe 158-1272,721,915 10/1955 Huntley 200-137 3,132,805 5/ 1964- I T-ramontini etal. 236-102 3,155,144 11/1964 Budlane 158-123 2,185,436 1/1940 Gordon158-117.1 3,207,204 9/1965 Thompson 158-128 BERNARD A. GILHEANY, PrimaryExaminer.

H. A. LEWITTER, Assistant Examiner.

7. IN A FUEL BURNER UNIT HAVING A FUEL BURNER OUTLET PORT MEANS, MEANSFOR CONTROLLING THE FUEL SUPPLY TO THE UNIT, AND MEANS FOR INITIATINGCOMBUSTION OF THE FUEL TO PRODUCE A BURNER FLAME; A TEMPERATURERESPONSIVE DEVICE COMPRISING, AN ELONGATE TEMPERATURE DIFFERNENTIALEXPANSION MEMBER HAVING A NON-CIRCULAR CROSS SECTION AND BEING FORMEDFROM A SINGLE PIECE OF SHEET MATERIAL OF RELATIVELY LOW THERMALCONDUCTIVITY, SAID MEMBER INCLUDING A BASE WALL SECTION ADAPTED TO BEDISPOSED IN THE VICINITY OF THE BURNER OUTLET PORT MEANS WHEREIN THEBURNER FLAME WILL IMPINGE UPON THE BASE WALL SECTION AND A PAIR OF SIDEWALL SECTIONS EACH HAVING ONE LONGITUDINAL EDGE INTEGRALLY JOINED TOSAID BASE WALL SECTION, SAID MEMBER SUPPORTED AT ONE END AND FREE AT THEOTHER END, A SWITCH ACTUATOR ARM, SAID ARM RIGIDLY ATTACHED AT ONE ENDOF THE FREE END OF SAID MEMBER AND THE OTHER END OF SAID ARM EXTENDINGTHROUGH SAID MEMBER BEYOND THE SUPPORTED END THEREOF, AND SWITCHACTUATING MEANS ON SAID OTHER END OF SAID ARM.